Precipitation climatology of Lake Michigan Basin

Abstract

Average annual precipitation over Lake Michigan (29.6 inches) is 6 percent less than that of the land portion of the basin.The results of this comprehensive study are more valid than those of previous studies, which estimated lake and land precipitation as equal, because they are based on more detailed land and lake data and greater knowledge of lake effects.The best possible measures of average seasonal and annual precipitation for the lake and the basin are determined from three detailed studies of thunderstorms, hailstorms, and snowfall combined with lake-land ratios (based on upwind land data rather than commonly used downwind data).The lake suppresses thunderstorm activity by 20 percent in summer, but in the fall increases it by 50 percent and also causes 400 percent more hail days in lower Michigan.Lake effects cause 25 to 100 percent greater snowfall along the eastern shore.Average lake precipitation is 4 percent higher in winter, 7 percent lower in spring, and 14 percent lower in summer than basin land precipitation; they are equal in fall.